GeoTIFF workflow, How are you currently calibrating GeoTIFF images? Options

[Dan Foster]

I just downloaded some collarless 24K DRGs from Minnesota DNR - http://deli.dnr.state.mn.us/

The TIFFs don't have an accompanying .tfw (worldfile) with calibration data. These are GeoTIFFs, so presumably the calibration info is stored inside the TIFF itself. Since ExpertGPS doesn't [yet] read calibration data out of GeoTIFFs, how are you currently dealing with these image files? Are you using another program to extract the calibration data, and create a .tfw? Are you just calibrating by hand?

[Jeremiah J. Burt...]

I've just done it by hand, but it would be nice if Expert could extract it.

jjb

[Chris Bolstad]

I specifically avoid the dataset you are talking about BECAUSE it doesn't have tfw files. On the rare occassion I need a DRG (99% of the time, I just use the terraserver topos), I try to find another source that includes a tfw, but as a last resort I calibrate by hand.

Chris Bolstad

[Tim Osborn]

Here's how it can be easily done if a program is GeoTiff unaware:

Go to http://fwtools.maptools.org/ and download FWTools1.3.1. You are going to need it for the tile making program I'm about to release anyway, and its contains a very useful set of utilities and libraries. For example with the utility gdalwarp.exe, you can change the projection of an existing image...and it will do the necessary warping of the pixels (wow!).

FWTools will install in your Program Files folder. Another one of the command-line executables in the FWTools1.3.1/bin folder is listgeo.exe. You can use it to create a world file for a GeoTIFF file that doesn't have one already. To use it, invoke the "FWTools Shell" from the icon that was created on your desktop. That will temporarily set the necessary environment variables (path, etc) for FWTools. Then at the command prompt type "listgeo -tfw c:\mygeotifffile.tif". Replace the "c:\mygeotifffile.tif" part with the filename of the geotiff of interest. This will produce an ESRI world file. Without the -tfw flag, the metadata for the GeoTiff will be displayed to the console.

Documentation for listgeo.exe is located at http://remotesensing.org/geotiff/listgeo.html:

[Chris Bolstad]

Mentor Software has a bunch of freebies that they distribute as promotional items. There are a bunch of converters etc, for coordinate and datum conversion and other handy utilities. I downloaded these last winter but had completely forgot about them when this thread started. One of the utilities is GeoTiffExaminer, which will create a tfw file from a Geotiff or convert a tiff with tfw to a geotiff. Another one of the utilities that I actually do use alot is "State Plane Zone Locator" which lets you determine the state plane and FIPS code for any county in the US. There are some other utilities that are a bit above my head but may be useful to people who know what they are doing like "Roll Your Own Molendesky".

Chris Bolstad

[Tim Osborn]

I agree. Mentor Software has a number of useful mini-utilities.

However, be careful with Geotiffexaminer. Under certain conditions it will create an erroneous world file. It does this whenever it sees a geotiff that contains ModelTiepointTag information that references any position other than the upper left corner of the image. Manifold GIS software currently has the same problem, but it has been acknowledged and is being fixed. It looks to me like there is no further development occuring for the Mentor Software utilities. For the truly curious, the painful details of the nature of the error is at http://69.17.46.171/Site/Thread.aspx?id=42...197520369370000 where I finally figured it out in post #42976.

If you need to create a world file from a geotiff, I would stick with the listgeo utility. It works correctly regardless of the position of the ModelTiepointTag in the geotiff file.

Tim